Background and aim: To evaluate the convergent and discriminative validity of many continuous composite disease activity indices and patient-reported outcome measures (PROMs) in rheumatoid arthritis (RA).
Methods: In consecutive RA patients in moderate or high disease activity, according to the Simplified Disease Activity Index (SDAI) definition, were computed four additional composite disease activity indices, the 28-joint Disease Activity Score - erythrocyte sedimentation rate (DAS28-ESR), the Clinical Disease Activity Index (CDAI), the Chronic Arthritis Systemic Index (CASI), and the Mean Overall Index for RA (MOI-RA), and five PROMs, the Patients' Activity Scale (PAS), the Rheumatoid Arthritis Impact of Disease (RAID), the 5-item RA Disease Activity Index (RADAI-5), the Routine Assessment of Patient Index Data (RAPID3), and the Clinical Arthritis Activity (PRO-CLARA). Spearman's rho correlation coefficients were determined to assess their convergent validity, and discriminative performance was calculated by the area under the receiver-operating curve (AUC-ROC). The patients' opinion of their symptomatic status (PASS) was used as the external criterion.
Results: 246 RA patients with moderate (29.3%) or high disease activity (70.7%) have been assessed. The indices all showed a significant correlation (p <0.0001 for all). Among the composite disease activity indices, the CDAI was the one that showed the best discriminating ability compared to the PASS (AUC = 0.962), while among the PROMs the RAID was the most performing (AUC = 0.879).
Conclusions: CDAI as composite index of disease activity, and RAID as PROM, are the two instruments with the best performances in relation to PASS. The use of validated disease activity measures can help in clinical practice to adopt treat-to-target strategies in RA patients. (www.actabiomedica.it).